Many modern telephone sets have the dial located in the handset with the transmitter and receiver, instead of located in the permanently positioned base, thereby giving the telephone user greater mobility while using the telephone set. One such telephone set is the Trimline.RTM. Telephone Set manufactured by the Western Electric Co., Inc. of New York, N.Y.
Since the dial is located in the handset, only the length of the handset cord limits the dialing convenience of a telephone user. Also included in the telephone handset is a push-button switch which when depressed opens the tip and ring lead connection between the telephone handset and the user's telephone line, thereby terminating the present connection. Release of the button switch reconnects the tip and ring leads of the telephone handset with the user's telephone line, thereby establishing a second connection to receive dial tone. Thus the pushbutton switch located in the handset and electrically connected in series with the base mounted switch hook affords the user greater mobility since not only can the user dial by using the handset dial, but a first connection can be terminated and a second dial tone connection established by depressing and releasing the pushbutton switch located on the handset.
A fully mobile telephone set, that is one which can be operated independent of a base, is useful in a hospital environment where a patient can keep the telephone set on the bed and not need to return it to the permanently mounted base. In this environment it is necessary that the telephone set be able to operate in three modes, ON-HOOK, OFF-HOOK and temporary ON-HOOK. In conventional practice when a telephone set is considered ON-HOOK the set's receiver, transmitter and dial circuitry are disconnected from the telephone line with only the ringer circuit closed, and when "ON-HOOK" it is connected to the telephone line. Temporary ON-HOOK permits the user to easily break an existing connection, e.g., terminate an existing call, and establish a second connection, e.g., establish a new dial tone connection. Further, the telephone set must have a ringing indication to signal the user of an incoming call.
To achieve a partially mobile telephone handset, the handset has been made somewhat independent of the switch-hook typically positioned in the permanently positioned base by locating a switch-hook arrangement in the handset as described in the patent of C. Kowaleski, U.S. Pat. No. 3,396,244 issued on Aug. 6, 1968. This arrangement features a double-acting mechanical push-button type switch which operates to retain the set in either an ON-HOOK or OFF-HOOK mode without having to return the set to its base mounted cradle. Although the switch arrangement described in the Kowaleski patent does permit the handset to be operated in either an ON-HOOK or OFF-HOOK mode independent of the base, the mechanical switch used in Kowaleski has elaborate mechanical linkages and adds considerable expense to the cost of manufacturing the handset.
Another approach to increasing utility and mobility of the dial-in-handset telephone is adding a logic and control circuit to the handset for effecting ON-HOOK and OFF-HOOK operations as described by Greeman et al. in their U.S. Pat. No. 3,489,860 issued Jan. 13, 1970. However, these additional electronics add to the cost and the circuit complexity of the telephone set.
There is a need, therefore, for a dial-in-handset telephone having complete flexibility independent of a base that is easy to operate, economical to manufacture and containing no new complex circuitry.